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Proton exchange membrane (PEM) fuel cells are ideal power sources with great potential for automobiles, backup power systems and stationary applications, owing to high efficiency, zero emissions and high power density. For these devices with large power consumption, many unit cells are assembled in series to construct a stack to provide the required voltage and power. However, the assembly process remains a major obstacle to the large-scale deployment of high-power stack. The performance and durability of stacks are greatly affected by the assembly procedures, and the impact mechanism and assembly technique need to be fully understanding. This paper presents an overview of important issues related to the assembly process of fuel cell stacks, providing a basis for engineers and researchers to improve stack performance. It begins with a description of quality evaluation of the stack assembly, followed by assembly methods to clarify the history of the development of stack design. The main contributions to in-situ behavior of stack during the assembly compression and dynamic compression is presented in detail. Numerical methods and optimization techniques are analyzed to guide assembly process. Finally, novel stack designs involving the assembly process are sorted out. A summary of the key points in this area is also provided as a direction for future work. The aim of this paper is to evaluate which factors affect the cell performance during assembly process and how adverse effects should be mitigated via mechanism analysis, quality evaluation, assembly method selection, process optimization and novel stack structure design. • Optimization method should be proposed to balance eight quality evaluation metrics. • Stack adaptability and endplate integration are orientation of assembly methods. • Micro scale model should be improved with the consideration of GDL fiber structure. • Complete stack model combining material features and multiscale dimensions is lack. • Accumulated manufacturing errors cause uneven performance of unit cells. [ABSTRACT FROM AUTHOR]

Proton exchange membrane (PEM) fuel cells are promising zero-emission power source for automobiles, portable devices, backup power system and stationary applications. However, their relatively short lifespan remains a major obstacle to the commercial deployment of this type of fuel cell. The membrane's mechanical degradation is the main cause of early-stage failure in fuel cell lifetimes. In order to provide engineers and researchers with a basis for extending fuel cell durability, this paper presents an overview of important issues relating to mechanical failure and mitigation strategies for PEM fuel cell membranes, drawing on a survey of the existing literature. This review begins with a sketch of failure mechanisms in an effort to establish an unambiguous definition of membrane degradation in each stage of its lifespan. The material properties of typical membranes are outlined below to illustrate the fundamentals of their mechanical behavior and cell degradation. Following the lifespan of a membrane, the causes and mechanisms of mechanical degradation in the fabrication process, cell assembly process, short-term phase and long-term phase of cell operation are discussed in detail. Practical strategies for reducing the degradation rate are introduced to each process. Finally, in-situ and ex-situ methods for the evaluation and characterization of mechanical durability are summarized to pursue the measurement methods and protocols of membranes. The aim is to assess which mechanisms affect the mechanical failure of membranes and how degradation should be mitigated across the entire lifetime of fuel cells. A summary of further work in this area is also provided to give a direction to future research. • Mechanical degradation of membranes across fuel cell's lifetime are discussed. • Mitigated strategies for failure are proposed for each stage of membrane's lifespan. • A standard set of evaluation method and protocol for membrane durability is discussed. • A summary of key points and research interests is given based on our understanding. [ABSTRACT FROM AUTHOR]